Xen Project Software Overview: Difference between revisions
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To boost performance, fully virtualized HVM guests can use special paravirtual device drivers (PVHVM or PV-on-HVM drivers). These drivers are optimized PV drivers for HVM environments and bypass the emulation for disk and network IO, thus giving you PV like (or better) performance on HVM systems. This means that you can get optimal performance on guests operating systems such as Windows. |
To boost performance, fully virtualized HVM guests can use special paravirtual device drivers (PVHVM or PV-on-HVM drivers). These drivers are optimized PV drivers for HVM environments and bypass the emulation for disk and network IO, thus giving you PV like (or better) performance on HVM systems. This means that you can get optimal performance on guests operating systems such as Windows. |
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Note that Xen Project PV (paravirtual) guests automatically use PV drivers: there is thus no need for these drivers - you are already automatically using the optimized drivers. PVHVM drivers are only required for |
Note that Xen Project PV (paravirtual) guests automatically use PV drivers: there is thus no need for these drivers - you are already automatically using the optimized drivers. PVHVM drivers are only required for HVM (fully virtualized) guest VMs. |
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'''Also see:''' |
'''Also see:''' |
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=== PV in an HVM Container (PVH) - New in Xen Project 4.4 === |
=== PV in an HVM Container (PVH) - New in Xen Project 4.4 === |
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Xen Project 4.4 introduced a virtualization mode called PVH. This is essentially a PV guest using PV drivers for boot and I/O. Otherwise it uses HW virtualization extensions, without the need for emulation. PVH is considered experimental in 4.4; it works pretty well, but additional tuning is needed (probably in the 4.5 release) before it should be used in production. PVH has the potential to combine the best trade-offs of all virtualization modes, while simplifying the Xen architecture. |
Xen Project 4.4 introduced a virtualization mode called PVH. This is essentially a PV guest using PV drivers for boot and I/O. Otherwise it uses HW virtualization extensions, without the need for emulation. PVH is considered experimental in 4.4; it works pretty well, but additional tuning is needed (probably in the 4.5 release) before it should be used in production. PVH has the potential to combine the best trade-offs of all virtualization modes, while simplifying the Xen architecture. |
Revision as of 21:06, 17 April 2014
Features |
Xen Project Features |
Xen Project-enabled Kernels |
Xen Project-Enabled operating systems |
PV-Enabled operating systems |
Xen Kernel Feature Matrix |
Guest types |
Paravirtualization (PV) |
HVM |
PV on HVM |
PV on HVM Drivers |
Information about using PV-on-HVM drivers |
HowTo on PV-on-HVM drivers |
GPLPV Windows drivers |
Toolstacks |
Choice of ToolStacks |
Xen Project or XCP? |
Host Install |
Host OS Install Considerations |
Installing Hosts |
Live CDs, DVDs, etc. |
Guest Install |
Installing Guests |
Guest VM Images |
What is the Xen Project Hypervisor?
The Xen Project hypervisor is an open-source type-1 or baremetal hypervisor, which makes it possible to run many instances of an operating system or indeed different operating systems in parallel on a single machine (or host). The Xen Project hypervisor is the only type-1 hypervisor that is available as open source. It is used as the basis for a number of different commercial and open source applications, such as: server virtualization, Infrastructure as a Service (IaaS), desktop virtualization, security applications, embedded and hardware appliances. The Xen Project hypervisor is powering the largest clouds in production today.
Here are some of the Xen Project hypervisor's key features:
- Small footprint and interface (is around 1MB in size). Because it uses a microkernel design, with a small memory footprint and limited interface to the guest, it is more robust and secure than other hypervisors.
- Operating system agnostic: Most installations run with Linux as the main control stack (aka "domain 0"). But a number of other operating systems can be used instead, including NetBSD and OpenSolaris.
- Driver Isolation: The Xen Project hypervisor has the capability to allow the main device driver for a system to run inside of a virtual machine. If the driver crashes, or is compromised, the VM containing the driver can be rebooted and the driver restarted without affecting the rest of the system.
- Paravirtualization: Fully paravirtualized guests have been optimized to run as a virtual machine. This allows the guests to run much faster than with hardware extensions (HVM). Additionally, the hypervisor can run on hardware that doesn't support virtualization extensions.
This page will explore the key aspects of the Xen Project architecture that a user needs to understsand in order to make the best choices.
- Guest types: The Xen Project hypervisor can run fully virtualized (HVM) guests, or paravirtualized (PV) guests.
- Domain 0: The architecture employs a special domain called domain 0 which contains drivers for the hardware, as well as the toolstack to control VMs.
- Toolstacks: This section covers various toolstack front-ends available as part of the Xen Project stack and the implications of using each.
Introduction to Xen Project Architecture
Below is a diagram of the Xen Project architecture. The Xen Project hypervisor runs directly on the hardware and is responsible for handling CPU, Memory, and interrupts. It is the first program running after exiting the bootloader. On top of the hypervisor run a number of virtual machines. A running instance of a virtual machine in Xen is called a domain or guest. A special domain, called domain 0 contains the drivers for all the devices in the system. Domain 0 also contains a control stack to manage virtual machine creation, destruction, and configuration.
Components in detail:
- The Xen Project Hypervisor is an exceptionally lean (<150,000 lines of code) software layer that runs directly on the hardware and is responsible for managing CPU, memory, and interrupts. It is the first program running after the bootloader exits. The hypervisor itself has no knowledge of I/O functions such as networking and storage.
- Guest Domains/Virtual Machines are virtualized environments, each running their own operating system and applications. Xen Project supports two different virtualization modes: Paravirtualization (PV) and Hardware-assisted or Full Virtualization (HVM). Both guest types can be used at the same time on a single Xen Project system. It is also possible to use techniques used for Paravirtualization in an HVM guest: essentially creating a continuum between PV and HVM. This approach is called PV on HVM. Xen guests are totally isolated from the hardware: in other words, they have no privilege to access hardware or I/O functionality. Thus, they are also called unprivileged domain (or DomU).
- The Control Domain (or Domain 0) is a specialized Virtual Machine that has special privileges like the capability to access the hardware directly, handles all access to the system’s I/O functions and interacts with the other Virtual Machines. It also exposes a control interface to the outside world, through which the system is controlled. The Xen Project hypervisor is not usable without Domain 0, which is the first VM started by the system.
- Toolstack and Console: Domain 0 contains a control stack (also called Toolstack) that allows a user to manage virtual machine creation, destruction, and configuration. The toolstack exposes an interface that is either driven by a command line console, by a graphical interface or by a cloud orchestration stack such as OpenStack or CloudStack.
- Xen Project-enabled operating systems: Domain 0 requires a Xen Project-enabled kernel. Paravirtualized guests require a PV-enabled kernel. Linux distributions that are based on recent Linux kernel are Xen Project-enabled and usually contain packages that contain the Xen Project Hypervisor and Tools (the default Toolstack and Console). All but legacy Linux kernels are PV-enabled, capable of running PV guests.
Also see:
- Xen Project Features
- Xen-Project Enabled operating systems
- PV-Enabled operating systems
- Availability of Xen Project Functionality on Linux Kernel (by version)
Guest Types
Xen Project supports running two different types of guests: Paravirtualization (PV) and Full or Hardware assisted Virtualization (HVM). Both guest types can be used at the same time on a single hypervisor. It is also possible to use techniques used for Paravirtualization in an HVM guest: essentially creating a continuum between PV and HVM. This approach is called PV on HVM.
Also see:
Xen Project Paravirtualization (PV)
Paravirtualization is an efficient and lightweight virtualization technique originally introduced by Xen Project, later adopted by other virtualization platforms. PV does not require virtualization extensions from the host CPU. However, paravirtualized guests require a PV-enabled kernel and PV drivers, so the guests are aware of the hypervisor and can run efficiently without emulation or virtual emulated hardware. PV-enabled kernels exist for Linux, NetBSD, FreeBSD and OpenSolaris. Linux kernels have been PV-enabled from 2.6.24 using the Linux pvops framework. In practice this means that PV will work with most Linux distributions (with the exception of very old versions of distros).
Also see:
Xen Project Full Virtualization (HVM)
Full Virtualization or Hardware-assisted virtualizion uses virtualization extensions from the host CPU to virtualize guests. HVM requires Intel VT or AMD-V hardware extensions. The Xen Project software uses Qemu to emulate PC hardware, including BIOS, IDE disk controller, VGA graphic adapter, USB controller, network adapter etc. Virtualization hardware extensions are used to boost performance of the emulation. Fully virtualized guests do not require any kernel support. This means that Windows operating systems can be used as a Xen Project HVM guest. Fully virtualized guests are usually slower than paravirtualized guests, because of the required emulation.
PV on HVM
To boost performance, fully virtualized HVM guests can use special paravirtual device drivers (PVHVM or PV-on-HVM drivers). These drivers are optimized PV drivers for HVM environments and bypass the emulation for disk and network IO, thus giving you PV like (or better) performance on HVM systems. This means that you can get optimal performance on guests operating systems such as Windows.
Note that Xen Project PV (paravirtual) guests automatically use PV drivers: there is thus no need for these drivers - you are already automatically using the optimized drivers. PVHVM drivers are only required for HVM (fully virtualized) guest VMs.
Also see:
- More Information...
- Information about using PV-on-HVM drivers
- HowTo on PV-on-HVM drivers
- Xen Project Windows HVM guests can use the opensource GPLPV drivers
PV in an HVM Container (PVH) - New in Xen Project 4.4
Xen Project 4.4 introduced a virtualization mode called PVH. This is essentially a PV guest using PV drivers for boot and I/O. Otherwise it uses HW virtualization extensions, without the need for emulation. PVH is considered experimental in 4.4; it works pretty well, but additional tuning is needed (probably in the 4.5 release) before it should be used in production. PVH has the potential to combine the best trade-offs of all virtualization modes, while simplifying the Xen architecture.
For more info see:
- PVH: PV Guest in HVM container (presentation)
- Xen on ARM Cortex A15 (presentation) - also uses PVH
- PVH: PV Guest in HVM container (video)
- Xen on ARM Cortex A15 (video) - also uses PVH
Toolstacks, Managment APIs and Consoles
Xen can run with a number of different toolstacks. Each toolstack exposes an API, which will run different tools. The figure below gives a very brief overview of the choices you have, which commercial products use which stack and examples of hosting vendors using specific APIs.
In short: Xen can be run with the default toolstack, with Libvirt and with XAPI. When Xen is run with XAPI, we tend to call the resulting stack XCP. The diagram above shows the various options: all of them have different trade-offs and are optimized for different use-cases. However in general, the more on the right of the picture you are, the more functionality will be on offer.
Which to Choose?
- The article Choice of ToolStacks gives you an overview of the various options, with further links to tooling and stacks for a specific API exposed by that toolstack.
- Xen or XCP also provides good pointers on whether to use Xen or XCP.
Of course there are also additional management tools available for different API's. For more information see:
Xen:
- Xen Management Tools
- Open Source Tools and Software interfacing with Xen
- Commercial Tools and Software interfacing with Xen
XCP:
- XCP Management Tools
- Open Source Tools and Software interfacing with XCP
- Commercial Tools and Software interfacing with XCP
Getting Xen, Host and Guest Install
Choice of Control Domain (Dom0)
As stated earlier, Xen requires a kernel as control domain. Most Xen-enabled kernels are very similar from the perspective of Xen. Choosing the right Dom0 for you comes down to:
- How familiar you are with a specific distro (e.g. packaging system, etc.)
- Xen Hypervisor version that ships with the distro
- Whether you can get commercial support (if you need it)
If you use XCP, you typically will not be interfacing much with Dom0. That is unless you are a power user.
Also See
Getting Xen
The Xen hypervisor is available as source distribution from Xen.org. However, you can get recent Xen binaries as packages from many Linux and Unix distributions, both open source and commercial. The Xen Cloud Platform ISOs also contain the Xen Hypervisor in binary form.
Xen Source Distributions The Xen community delivers the Xen hypervisor as a source distribution, following the delivery model of the Linux kernel. Xen is released approximately once a year, with several update releases per year containing security fixes and critical bug fixes. To build Xen from source, you can either download a Xen source release or you can fetch the source tree from the source repository. Each Xen source release and the Xen source tree contain a README file in the root directory, with detailed build instructions for the Xen hypervisor. The release notes for Xen distributions also contain build instructions and so does the Compiling Xen page.
Xen Cloud Platform The Xen Cloud Platform (or XCP) is a binary distribution of Xen that contains the Xen Hypervisor, a pre-packaged and configured Control Domain and the powerful Xen API toolstack and management API. XCP can be installed from either a single installable ISO, or by running
apt-get install xcp-xapi
on a Debian-based Linux distribution.
XCP delivers an enterprise-ready, server virtualization and cloud computing platform with lots of additional management functionality compared Xen: with XCP you can manage pools of host systems, use advanced storage repositories, and take advantage of advanced performance monitoring capabilities. Download here!
Xen in Linux/Unix Distributions Most Linux and many Unix distributions contain built binaries of Xen that can be downloaded and installed through the native package management system. If your Linux/Unix distribution includes Xen and a Xen-enabled kernel, we recommend to use them as you will benefit from ease of install, good integration with the distribution, support from the distribution, provision of security updates etc. Installing Xen in a distribution typically requires the following basic steps: a) Install your favourite distribution, b) Install xen package(s) or meta-package, c) check boot settings and d) reboot. After the reboot, your system will run your favourite Linux/Unix distribution as Control Domain on top of the Xen Hypervisor.
Host and Guest Install
The following documents
- Category:Host Install contains guides on how to install a control domain for various Linux/Unix distros
- Category:Guest Install contains guides on how to install a variety of guests for various Linux/Unix distros
This table contains a list of Xen Project resources for various Linux and Unix distributions. |
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Distro | Main website | Description | Resources |
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Arch Linux | archlinux.org | Arch Linux is a lightweight and flexible Linux® distribution that tries to “keep it simple”. |
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Alpine Linux | alpinelinux.org | A security-oriented, lightweight Linux distribution based on musl libc and busybox. |
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CentOS 5 | centos.org | CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise Linux vendor. CentOS conforms fully with the upstream vendor's redistribution policy and aims to be 100% binary compatible. (CentOS mainly changes packages to remove upstream vendor branding and artwork.) CentOS is free. |
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CentOS 6 | centos.org | CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise Linux vendor. CentOS conforms fully with the upstream vendor's redistribution policy and aims to be 100% binary compatible. (CentOS mainly changes packages to remove upstream vendor branding and artwork.) CentOS is free. |
CentOS 6.0 - 6.3 does not include Xen Project software, but you can get support from various sources. The following articles may be useful
CentOS 6.4+ does include Xen Project support and can be used as a dom0 and domU out-of-the-box, thanks to the Xen4CentOS project Xen packages in CentOS 6 and commercial support are also available from "Xen made easy!"
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Debian | debian.org | The Debian project produces an entirely free operating system that empowers its users to be in control of the software running their computers. |
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Fedora | fedoraproject.org | Fedora is a RPM-based distribution with a 6-month release cycle, and is the community-supported base of RHEL releases. |
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FreeBSD | freebsd.org | FreeBSD® is an advanced operating system for modern server, desktop, and embedded computer platforms. |
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Finnix | finnix.org | Finnix is a sysadmin utility Linux LiveCD, and includes out-of-the-box Xen Project guest support. |
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Gentoo Linux | gentoo.org | Gentoo Linux is a special flavor of Linux that can be automatically optimized and customized for just about any application or need. Extreme performance, configurability and a top-notch user and developer community are all hallmarks of the Gentoo experience. |
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NetBSD | netbsd.org | NetBSD is a free, fast, secure, and highly portable Unix-like open source operating system. |
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Oracle Linux | oracle.com | Oracle Corporation distributes Oracle Linux the Unbreakable Enterprise Kernel. Oracle states that the Unbreakable Enterprise Kernel is compatible with RHEL, Oracle middleware and 3rd-party RHEL-certified applications. Oracle Linux supports KVM, Xen Project, and Oracle VM Server for x86, which is based on Xen. |
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openSuSE | opensuse.org | openSuSE is a free and Linux-based operating system for your PC, Laptop or Server. |
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Red Hat Enterprise Linux (RHEL) 5.x | redhat.com | RHEL 5.x includes the Xen Project 3.4 Hypervisor as well as a Xen Project-enabled kernel, and can be used as a dom0 and domU |
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Red Hat Enterprise Linux (RHEL) 6.x | redhat.com | RHEL 6.x does not include the Xen Project Hypervisor. But, a Dom0 capable kernel, Xen Project hypervisor, and libvirt packages for use with RedHat Enterprise Linux 6 and its derivatives are available from either the Xen4CentOS project or the "Xen made easy!" effort. |
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Ubuntu | ubuntu.com | Fast, secure and stylishly simple, the Ubuntu operating system is used by 20 million people worldwide every day. |
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Getting Help!
The Xen community are helpful and friendly people. We are here for you. There are several ways to get help and keep on top of what is going on!
- Read News!
- Read Documentation!
- Contact other users, to ask the questions and discuss Xen, XCP or other Xen related projects
News Sources
- Xen Home page aggregates selected news stories and blog posts
- The Xen Blog covers technical and community related stories
- xen-announce mailing list is a low frequency mailing list for important announcements
Documentation
Documentation for projects hosted on Xen.org is available on the Xen Wiki. Our wiki is active and community maintained. It contains a lot of useful information and uses categories extensively to make it easy to find information. You may also want to check:
- Category:Manual
- Category:HowTo
- Category:FAQ
- For more applicable categories, see the front page
Mailing Lists
Search Mailing Lists All Xen.org mailing lists are archived using the MarkMail system at xen.markmail.org. Before you ask a question, it is worth checking whether somebody else has asked the question before
Main Mailing Lists Xen.org maintains a number of mailing lists for users of Xen, the Xen Cloud Platform and other projects. English is used by readers on this list.
- xen-users is the list for technical support and discussions for the Xen hypervisor. If you are not sure where your question belongs start here!
- xen-api is the list for technical support and discussions for the Xen Cloud Platform (XCP).
- xen-arm is the list for technical support and discussions for the Xen ARM project.
IRC
Internet Relay Chat (IRC) is a great way to connect with Xen community members in real time chat and for support.
- ##xen is the channel for technical support and discussions for the Xen hypervisor. If you are not sure where your question belongs start here!
- Check out our IRC page if you are not familiar with IRC.
Other places
There are a number of other places, where you can get help on Xen and XCP. For example:
- Xen Questions on serverfault
- XCP & XenServer Questions on serverfault
- Many Linux Distributions that support Xen have a dedicated list - see the table in this link
Raising Bugs
If you find a bug, you can report bugs against Xen, or the Xen Cloud Platform. Before you raise a bug, please read Reporting Bugs!
Roadmaps, Release Cadence, Maintenance Releases
The xen.org community aims to release the Xen Hypervisor on an approximate cadence of 9 months. Roadmap information is tracked at Xen Roadmap. You can find information on the maintenance releas cycle at Xen Maintenance Releases.
Also See
Installation
- Getting Started guides a new user through key decisions to be made
- Category:Host Install contains guides on how to install a control domain
- Category:Guest Install contains guides on how to install a variety of guests
- Category:Host Configuration contains documents related to bootloader, console and network configuration
- Guest VM Images provides pointers to various preinstalled guest images.
- LiveCD provides pointers to Live CDs for Xen
Release Information
- Category:Manual contains Xen manual documents
- Category:Release Notes contain Xen release notes
- Xen Release Features contains a matrix of features against Xen versions
- Category:Xen 4.2 contain articles related to Xen 4.2 features, benchmarks, planning, etc.
Specialist Topics: Networking, Performance, Security, NUMA, VGA, ...
Specialist topics on Xen:
- Category:Networking contains articles related to networking
- Category:NUMA contains all articles related to the running (or to improving the support for doing so) of the Xen Hypervisor on NUMA architectures
- Category:Performance contains documents, tuning instructions and benchmarks related to the performance of Xen, XCP, etc.
- Category:Security contains documents related to Xen, XCP, etc. security
- Category:VGA contains documents related to VGA, VTd, GPY passthrough, etc.
FAQs, HowTos, ...
- Category:FAQ contains Xen FAQs
- Category:HowTo contains various HowTo's
- Category:Tutorial contains various Tutorials
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